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Redox imbalance and oxidative stress in Mecp2 deficient neurons

dc.contributor.advisorMüller, Michael Prof. Dr.
dc.contributor.authorCan, Karolina
dc.titleRedox imbalance and oxidative stress in Mecp2 deficient neuronsde
dc.contributor.refereeMüller, Michael Prof. Dr.
dc.description.abstractengRett syndrome is a neurodevelopmental disorder that primarily occurs in girls with a prevalence of 1:10.000–1:15.000 life births. The main genetic reasons of Rett syndrome are mutations in the methyl-CpG binding protein 2 (<i>MECP2</i>) gene. After a short, but normal development, a Rett child falls into developmental stagnation, which is followed by neuronal and autonomic dysfunction, and manifests as mental retardation, breathing impairment, epilepsy, loss of speech, mobility disturbances and stereotypical hand movements. Growing evidence shows that Rett syndrome is associated with mitochondrial dysfunction and oxidation stress. Mitochondria of MeCP2-deficient (<i>Mecp2<sup>-/y</sup></i>) mouse brain have been previously confirmed to be partly uncoupled and to show increased respiratory rates. More oxidized baseline conditions, exaggerated responses to oxidants and mitochondrial inhibition have been detected in the hippocampus of <i>Mecp2<sup>-/y</sup></i> mice. To unveil the molecular causes of this redox imbalance specifically in neurons, and to enable a quantitative live-cell imaging of sub-cellular redox dynamics, viral vectors, expressing the genetically-encoded optical redox sensor reduction/oxidation-sensitive green fluorescent protein 1 (roGFP1) in cytosol and mitochondrial matrix have been generated. For quantitation, the ratiometric responses of roGFP1s were calibrated to full oxidation and reduction in mitochondrial and cytosolic compartments. Detailed fluorescence microscopy and two photon imaging confirmed that mitochondrial and cytosolic redox baselines were more oxidized in <i>Mecp2<sup>-/y</sup></i> hippocampal neurons. Redox challenge induced by hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) and severe hypoxia elicited intensified oxidizing and reducing transients in <i>Mecp2<sup>-/y</sup></i> neurons, respectively. Moreover, inhibition of superoxide dismutase (SOD) caused a less intense oxidation in <i>Mecp2<sup>-/y</sup></i> cytosol and mitochondria, suggesting a decreased efficiency of this scavenging enzyme in Rett mice. Interestingly, differences among wildtype (WT) and <i>Mecp2<sup>-/y</sup></i> mice were evident especially in the more complex organotypic slices, and they occurred already at neonatal stages in mitochondria and the cytosol. Furthermore, the current work is the first study, showing a pronounced shift towards more oxidizing conditions in <i>Mecp2<sup>-/y</sup></i> neurons in response to different neurotransmitters. Taking advantage of the recently generated transgenic mouse lines, stably expressing roGFP1 in neuronal cytosol, the redox changes could be also confirmed for hippocampal neurons of adult and symptomatic <i>Mecp2<sup>-/y</sup></i> mice. Taken together, roGFP1 responds reliably to oxidation and reduction, and it allows for semi-quantitative recordings of redox changes specifically in neurons. Since mitochondria are a primary source of reactive oxygen species (ROS), and the neuronal mitochondria of <i>Mecp2<sup>-/y</sup></i> hippocampus revealed a more oxidizing and more vulnerable redox balance, this supports the hypothesis that mitochondrial dysfunction underlies the oxidative burden in Rett syndrome and drives potentially disease progression. Moreover, the roGFP1 transgenic mice will extend quantitative redox imaging to all postnatal stages and more complex preparations. This will enable studying disease progression and redox conditions throughout the brain of maturing Rett and WT
dc.contributor.coRefereeSchild, Detlev Prof. Dr. Dr.
dc.subject.engRett syndrome, MeCP2, mitochondria, oxidative stress, roGFP1de
dc.affiliation.instituteGöttinger Graduiertenschule für Neurowissenschaften, Biophysik und molekulare Biowissenschaften (GGNB)de
dc.subject.gokfullBiologie (PPN619462639)de

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